1. Field of the Invention
The present invention provides a method for locally repairing dislodged, damaged or otherwise unacceptable coatings on coated articles. Specifically, the present invention relates to a method for repairing coated articles having an upper thermal barrier coated layer and a lower bondcoat layer, wherein a series of masking allows the local removal and replacement of the layers of the coating article with minimal cost and speed.
2. Description of the Prior Art
Certain components or articles, such as turbine engines, are subjected to significant temperature and pressure extremes and degradation by oxidation and corrosives. For example, in airplane gas turbine engines, the temperature of the combustion of gases may exceed 3000° F., higher than the melting points of many of the engine parts. To protect the article subjected to these extremes, it is a common practice to coat the article with a topcoat, typically a thermal barrier ceramic coatings (TBC). The TBC protects the article from these extremes while also affording the opportunity to improve the efficiency of the engine by allowing the increase in operating temperatures.
For full effectiveness of the articles efficiency, the TBC must be strongly adhered to the coated article. The articles generally use an adhesive metallic bondcoat for this purpose, deposited on the surface of the article. The metallic bondcoat is typically a diffusion aluminide or an oxidation-resistant alloy, which promotes the adhesion of the insulating TBC layer to the component while also inhibiting oxidation of the underlying article.
Despite the coatings, flaws may occur in the coated article or in the coatings themselves. Often local coating repair is necessitated by detection of base metal or bondcoat cracking due to low cycle fatigue (LCF) or thermal-mechanical fatigue (TMF) in service-run parts. In the instance that the coated article has a defective area and requires repair, the remnant bondcoat and TBC have to be removed to have access to the defective area, after which the defective area is repaired and bondcoat and TBC is reapplied. In the prior art, there is no preferred mode to address this situation. Typically, a substantial amount of the coated article is stripped and recoated, which forces removal of not only defective coatings but also extensive amounts of acceptable coatings. Prior art has taught local repair of topcoats, but typically only removal of a portion of TBC is required. See, for example, U.S. Pat. No. 6,235,352 to Leverant et al.
There is a need for a reliable and reproducible manufacturing method for local repair of defective coatings and/or partially or fully lost coatings in service or to repair cracked/defective coated articles. This need is extensive due to the high cost and relatively long turn around time associated with the current practice, which forces stripping and recoating not only of local defective coatings but of expensive, acceptable coatings as well. There is a need for a method for local repair of coating that is locally applied to defective areas.